<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>

    div{
      width: 300px;
      background-color: rgba(0,0,0,0.3);
      padding: 10px;
      overflow: hidden;
      position: relative;
    }
    input{
      border: none;
      width: 300px;
      padding: 10px 20px;
      box-sizing: border-box;
    }

    img{
      position: absolute;
      right: 30px;
      bottom: 30px;
    }
    p{
      font-size: 12px;
      color: red;
      margin: 0px;
    }


  </style>
</head>
<body>
<div>
  <input type="text" PLACEHOLDER="请输入用户名:">
  <img src="http://doc.canglaoshi.org/tstore_v1/images/login/yhm.png" alt="">
  <p>用户名不能为空</p>
</div>

</body>
</html>